Sensors are being developed for use in roads, bridges, dams, buildings, towers, and vehicles that may provide many different types of information, including displacement, strain, speed, acceleration, temperature, pressure, and force. Providing power to the sensors and communicating data from the sensors has been difficult. The present invention provides a way to more efficiently provide power for sensors and to communicate with sensors.
Inspection of civil structures are very important for public safety. Litigation costs due to structural failure not only hurts the department held responsible for the failure, but the litigation takes money away from other projects, which in turn, increases public risk by reducing monies available for future maintenance and inspections. We propose to develop an autonomous robotic sensor inspection system capable of remote powering and data collection from a network of embedded sensing nodes, and providing remote data access via the internet. The system will utilize existing microminiature, multichannel, wireless, programmable Addressable Sensing Modules (ASM's) to sample data from a variety of sensors. These inductively powered nodes will not require batteries or interconnecting lead wires, which greatly enhances their reliability and lowers costs.
Networks of sensing nodes can be embedded, interrogated, and remotely accessed in applications where visual inspection by people is not practical due to: physical space constraints, remote geographic locations, high inspection costs, and high risks involved for those performing the inspections. The sensors can indicate the need for repair, replacement, or reinforcement, which will reduce the risks of catastrophic failures and would be useful after natural disasters. Sensors of peak displacement, peak strain, corrosion, temperature, inclination, and other microelectromechanical sensors (MEMS), are now capable of embeddment in structures, and are compatible with our ASM's. The availability of critical structural health data on the internet would greatly assist highway engineers and scientists, to improve their working database on these structures, which will improve our understanding of the safety of civil structures and their requisite maintenance.
In the majority of civil structures, there is little data to help an engineer model the behavior of a structure before it is built or after rehabilitation. This leaves an engineer to rely on past experience to determine what type of repair to apply without truly knowing its affect on the physical strength of the structure. Physical measurements and on-site examinations are performed to assess structural integrity. Typically, maintenance and repairs are not performed until serious structural damage can be seen. In some cases, such as marine structures, damage occurs out of visual site where only specialized sensors can detect distress. Natural disasters such as floods, earthquakes, hurricanes, ice storms, and tornadoes, as well as everyday use, collisions, deicing salts, drainage, and corrosion compromise the safety of civil structures.
The soundness of on-site evaluations depends upon the people performing the inspection. The accuracy of the inspection depends on many factors: how thorough is the inspector, their ability to detect unsafe conditions, and the resources available-personnel, financial, equipment, and workload. Civil structures are large and can be located in unsafe and harsh environments. Traffic flow, structure height, the grade around the structure, underwater (pollution), and confined spaces (air poisoning) are a few obstacles inspectors have to overcome. Water pollution has made inspectors sick while checking bridge piers and abutments for scour. Seasonal thawing can increase river flow making bridge inspection dangerous. Steep embankments increase the risk of vehicle overturn. Having a way to interrogate embedded sensing nodes with multiple sensing elements (strain, temperature, vibration, depth, etc.) and inspect structures remotely would save time, equipment costs, personnel costs, and lower health risks to inspectors and the people using the structure.
Environmental influences such as scour, wind, waves, collisions, and corrosion weaken bridge integrity. Scour occurs when (1) sediment is carried away around bridge piers or abutments (2) sediment is removed from the bottom and sides of a river due to the bridge creating a narrower than natural channel for the river to flow through (3) and by everyday river flow carrying away sediment from the river bottom. Floods are the main cause of scour, eroding the ground that supports the bridge. Between the years 1961 and 1976, 46 of 96 major bridge failures were due to scour near piers. In 1987 the Interstate Highway bridge over Schoharie Creek in New York State collapsed killing 10 people, a total of 17 bridges were lost in New York that year due to scour. In 1989 a bridge over the Hatchie River in Covington, Tenn. failed due to scour killing 8 people.
Scour is measured using a number of techniques, such as: fathometers, fixed- and swept-frequency continuous seismic reflection profiling, and ground-penetrating radar. In each case an inspector has to be present to operate the equipment. The ability to monitor scour, as well as peak strain, during a flood using a remote interrogation process would increase safety, give real-time feedback, and potentially save lives.
Railroads provide another opportunity for remote monitoring of embedded sensors. Aug. 10, 1997 in Kingman, Ariz. an Amtrak passenger train derailed as it traveled on a bridge spanning a river. A storm suddenly moved in dumping 1.76″ of rain causing a flash flood. Inspectors had inspected the bridge not more than three hours before the accident, warning sensors located on the bridge failed to stop or warn the train of damage. Remote interrogation hardware could be used to test track continuity as well as measure truss integrity.
Sensors can be embedded in or placed on structures to record physical measurements. Buildings, such as the Millikan Library at Caltech and Factor Building at UCLA as well as dams (Winooski dam in Winooski, Vt.) have been gauged with fiber optic sensors to monitor performance. All of the sensors used rely on power being constantly supplied to the sensor to operate and cables (with connectors) must be embedded in the structure for power and communication. This works well when the structure is easily accessible and power is always available, or, if battery powered, the batteries can be replaced easily. But power is not always available at the time when readings are needed most and batteries can only be embedded if they can be recharged. If the structure is located in a remote area, data may not be accessible when needed. Embedding cable is costly and time consuming during manufacture. Cabling also elevates the risk of failure during everyday operation and disasters.
Presently there is neither a means nor a system that can remotely interrogate an array of independent sensing nodes located throughout a structure. “The Robotic Inspector” (ROBIN, U.S. Pat. No. 5,551,525) was developed at the Intelligent Robotics Lab at Vanderbilt University. ROBIN was developed to inspect man-made structures. Advantages of ROBIN are that it is highly mobile and has versatile fixtures. However, ROBIN carries specific sensors in its limited payload area and is also restricted by a power cord.
Visual/Inspection Technologies, Inc. developed a product called SPOT that uses a pan & tilt zoom camera for pipe inspection. Although SPOT can travel into areas that people cannot, it requires an on-site person for operation, it is only equipped with a camera, it can weigh up to 120 lbs., and SPOT is specific to pipe applications.
NASA has developed a robot to search Antarctica for meteorites and rocks. The robot “Amadeus Nomad” can travel in sever weather conditions which constantly impede human travel. Amadeus Nomad requires minimal human assistance but uses onboard sensors for inspection.
Insects, although possessed of severely limited computational abilities (very small brains) can deal effectively with their environment. An insect's ability to navigate, respond to hazards, and achieve its goals (finding food and a mate) puts any robot to shame. Behavior Control (developed by Prof. Rodney Brooks at MIT in 1986) attempts to encapsulate the computational efficiencies that insects and other organisms use to achieve their impressive results. Behavior Control has proven an effective robot programming strategy for handling dynamic and/or poorly modeled environments. Behavior Control's sensor based strategy produces robots that respond quickly to changing conditions, react robustly to unexpected situations, and degrade gracefully in the presence of sensor faults. The most visible recent success of the Behavior Control methodology was Sojourner, the Mars rover. Sojourner was the culmination of several years of development of Behavior Control robots (Rocky I through Rocky IV) at NASA's Jet Propulsion Laboratory, JPL.
There is a need for robust, insect-like, autonomous structural inspection systems which can be used with easily deployed or embedded sensing nodes; and for data collected from these structures to be readily over the Internet. None of the available systems provide power to the sensors and communicate data from the sensors as effectively as possible. Thus, a better system for powering sensors and storage devices, and for transmitting data gathered by sensors is needed, and this solution is provided by the following invention.